Ink set

ABSTRACT

An ink set includes a cyan ink composition containing C.I. pigment blue 15:6 or C.I. pigment blue 60 as a pigment and a magenta ink composition containing at least one quinacridone pigment selected from the group consisting of C.I. pigment violet 19, C.I. pigment red 122, C.I. pigment red 202, and C.I. pigment red 209, or a quinacridone solid solution pigment formed of at least two selected from the above group, as a pigment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/539,084 filed Aug. 11, 2009, which claimed the benefit of thefollowing Japanese Patent Application 2008/215056 filed Aug. 25, 2008the contents of which are incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to an ink set having a wide colorreproduction range (gamut), in particular, an ink set having a widecolor reproduction range of a blue region in a dark portion.

2. Related Art

As a color model, a CIE/L*a*b* color system is known. According to theCIE/L*a*b* color system, any color (spectrum) in a visible light regionthat can be observed by human beings is able to be expressed bychromaticity coordinates.

In three parameters (L*, a*, and b*) of the CIE/L*a*b* color system, L*denotes luminance (brightness) of a color, and a* and b* denotechromaticity representing hue and saturation, respectively. Here, L*=0means black, and L*=100 means white; a* means the position of a colorbetween red and green, wherein a negative value represents green, and apositive value represents red; and b* means the position of a colorbetween yellow and blue, wherein a negative value represents blue, and apositive value represents yellow. Since the L*a*b* color model isthree-dimensional, a color space is expressed by a three-dimensionalspace, wherein the luminance is shown on the vertical axis.

However, the L*a*b* color model is only an index for conceptuallyexplaining a color space, and the color reproduction range thereof haslimitation. That is, for example, in the case that an image is formed ona recording medium using a pigment-based ink or ink set, there is acolor that cannot be reproduced by the colors of the L*a*b* color model.

At the same time, ink compositions containing various pigments havinghigh chromogenicity have been proposed. JP-A-2006-282810 discloses thatan ink having high chromogenicity and being excellent in ink reliabilitysuch as ejection stability, storage stability, and clogging can beobtained by an ink composition containing a quinacridone solid solutionpigment, a polyether-modified polydimethylsiloxane compound, and water.JP-A-2007-186641 discloses that an ink excellent in ink reliability suchas printing quality, ejection stability, storage stability, and cloggingcan be realized by an ink composition containing a water-insoluble vinylpolymer, water, and a surface-treated pigment (yellow, magenta, or cyan)that is composed of a solid solution pigment formed of specific two ormore pigments and has a hydrophilic dispersing group bonded to thesurface thereof.

Incidentally, the color reproduction of a blue region in a dark portion,particularly, a region where the L* value is 20 or less, has limitation.That is, since it is difficult to exhibit chromaticity and saturationwhen the luminance is low, a color having an L* value of 20 or less andan a* value of 30 or more or a b* value of −75 or less in the CIE/L*a*b*color system, for example, a color of (L*, a*, b*) (19.4, 30.0, -72.6)or (L*, a*, b*) =(19.4, 37.6, -76.8), cannot be reproduced on an imagerecording medium with liquid droplets (ink).

SUMMARY

An advantage of some aspects of the invention is to provide an ink sethaving a wide color reproduction range, in particular, an ink set havinga wide color reproduction range of a blue region in a dark portion. Sucha color could not been reproduced with known ink sets.

The present inventors have conducted intensive studies and have foundthe fact that an ink set composed of a combination of an cyan inkcomposition containing C.I. pigment blue 15:6 or C.I. pigment blue 60 asthe pigment and a magenta ink composition containing aquinacridone-based pigment can extend the color reproduction range of ablue region in a dark portion having an L* value of 20 or less, inparticular, the fact that an ink set composed of a combination of ancyan ink composition containing C.I. pigment blue 15:6 as the pigmentand a magenta ink composition containing a quinacridone solid solutionpigment can produce a color having an L* value of 20 or less, an a*value of 30 or more, and a b* value of −75 or less. Such a color couldnot been reproduced with known ink sets. Accordingly, the invention isas follows:

(1) An ink set including

a cyan ink composition containing C.I. pigment blue 15:6 or C.I. pigmentblue 60 as a pigment, and

a magenta ink composition containing at least one quinacridone pigmentselected from the group consisting of C.I. pigment violet 19, C.I.pigment red 122, C.I. pigment red 202, and C.I. pigment red 209, or aquinacridone solid solution pigment formed of at least two selected fromthe above group, as a pigment;

(2) The ink set according to the above (1), wherein the pigmentcontained in the magenta ink composition is a quinacridone solidsolution pigment formed of at least two selected from the groupconsisting of C.I. pigment violet 19, C.I. pigment red 122, C.I. pigmentred 202, and C.I. pigment red 209;(3) The ink set according to the above (2), wherein the pigmentcontained in the magenta ink composition is a quinacridone solidsolution pigment formed of C.I. pigment violet 19 and C.I. pigment red202;(4) The ink set according to the above (3), wherein the quinacridonesolid solution pigment is formed such that the weight of the C.I.pigment violet 19 is larger than that of the C.I. pigment red 202;(5) The ink set according to the above (3) or (4), wherein thequinacridone solid solution pigment is formed such that the weight ratioof the C.I. pigment violet 19 to the C.I. pigment red 202 is from 70/30to 50/50;(6) The ink set according to any one of the above (1) to (5), whereinthe C.I. pigment violet 19 contained in the quinacridone solid solutionpigment is a y-type; and(7) A recording apparatus including the ink set according to any of theabove (1) to (6).

According to the ink set of the invention, a color having an L* value of20 or less, an a* value of 30 or more, and a b* value of −75 or less inthe CIE standard, which is a color that could not been reproduced withknown ink sets, can be reproduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings.

FIG. 1 shows the gamuts (color reproduction ranges) at L*=20 in Examples1 and 2 and Comparative Example 1.

FIG. 2 shows the gamuts (color reproduction ranges) at L*=20 in Examples3 and 4 and Comparative Example 2.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The invention is an ink set including a cyan ink composition containing,as a pigment, C.I. pigment blue 15:6 or C.I. pigment blue 60, and amagenta ink composition containing, as a pigment, at least onequinacridone pigment selected from the group consisting of C.I. pigmentviolet 19, C.I. pigment red 122, C.I. pigment red 202, and C.I. pigmentred 209, or a quinacridone solid solution pigment formed of at least twoselected from the above group.

The cyan ink composition and the magenta ink composition constitutingthe ink set of the invention will be described in detail below.

1. Pigment

Commercially available C.I. pigment blue 15:6 (hereinafter, abbreviatedto “P.B.15:6”) and C.I. pigment blue 60 (hereinafter, abbreviated to“P.B.60”) can be used in the cyan ink composition of the invention.

Furthermore, commercially available C.I. pigment violet 19 (hereinafter,abbreviated to “P.V.19”), C.I. pigment red 122 (hereinafter, abbreviatedto “P.R.122”), C.I. pigment red 202 (hereinafter, abbreviated to“P.R.202”), and C.I. pigment red 209 (hereinafter, abbreviated to“P.R.209”) can be used as the quinacridone pigment contained in themagenta ink composition.

The quinacridone solid solution pigment in the invention is formed of atleast two selected from the group consisting of P.V.19 (in the solidsolution, γ-type P.V.19 is preferred from the viewpoint ofchromogenicity), P.R.122, P.R.202, and P.R.209.

The combination composed of two or more quinacridone compounds is notparticularly limited, but, in the invention, a solid solution pigmentcomposed of a combination of P.V.19 and P.R.209, a combination of P.V.19and P.R.122, and a combination of P.V.19 and P.R.202 are preferred fromthe viewpoint of chromogenicity, and a solid solution pigment composedof a combination of P.V.19 and P.R.202 is particularly preferred.

In the solid solution pigment composed of P.V.19 and P.R.209, themixture ratio of P.V.19 : P.R.209 is preferably within a range of 10:90to 90:10, more preferably 15:85 to 85:15, and particularly preferably30:70 to 50:50. In the combination of P.V.19 and P.R.122, the ratio ispreferably within a range of 10:90 to 90:10, more preferably 15:85 to85:15, and particularly preferably 30:70 to 50:50. In the combination ofP.V.19 and P.R.202, the ratio is also preferably within a range of 10:90to 90:10, more preferably 15:85 to 85:15, and particularly preferably30:70 to 50:50. The solid solution pigment configured by thequinacridone pigment can provide a magenta ink composition that isexcellent in color reproduction in red and violet regions of highsaturation and high brightness. In particular, a solid solution pigmentcomposed of P.V.19 and P.R.202 in which the weight of the P.V.19 islarger than that of the P.R.202 is particularly excellent in colorreproduction in red and violet regions of high saturation and highbrightness.

The quinacridone solid solution pigment may be produced by any methodwithout particular limitation and is usually produced by a widely knownmethod. Specifically, a method disclosed in JP-A-11-49998,JP-A-2000-319534, or JP-A-2003-253150 can be used. In the invention, theterm “quinacridone solid solution pigment” refers to a pigment existingin a mixed crystal form (a state crystallized in a mixed state) ofmolecules of a plurality of quinacridone pigments and is different fromthose prepared by simply mixing two or more types of quinacridonepigments.

Furthermore, whether two or more quinacridone pigments are formed into asolid solution can be easily confirmed by X-ray diffraction analysis. Ina mere mixture of two types of quinacridone pigments, the X-raydiffraction pattern is equivalent to the sum of X-ray diffractionpatterns of each pigment, and the peak strength is proportional to theblending ratio. On the other hand, in a quinacridone solid solutionpigment, the diffraction pattern is original to the newly formedcrystal.

In the quinacridone solid solution pigment of the invention, the averageparticle diameter of the solid solution pigment is preferably in a rangeof 10 to 200 nm and more preferably 50 to 150 nm. An average particlediameter smaller than 10 nm may cause a decrease in weatherability, andan average particle diameter larger than 200 nm may cause precipitationand unstable ejection.

The content of the pigment in the ink composition of the invention ispreferably 0.1 to 15 mass % and more preferably 1 to 10 mass %, from theviewpoint of ink reliability such as ejection stability, storagestability, and clogging.

2. Components Other Than Pigments

The ink compositions of the invention may each contain any component, inaddition to the pigment, without particular limitation and preferablycontain the following components.

Any dispersant that can be used in pigment ink can be used withoutparticular limitation, and examples of the dispersant include cationicdispersants, anionic dispersants, nonionic dispersants, and surfactants.

Examples of the anionic dispersants include polyacrylic acid,polymethacrylic acid, acrylic acid/acrylonitrile copolymers, vinylacetate/acrylic acid ester copolymers, acrylic acid/alkyl acrylate estercopolymers, styrene/acrylic acid copolymers, styrene/methacrylic acidcopolymers, styrene/acrylic acid/alkyl acrylate ester copolymers,styrene/methacrylic acid/alkyl acrylate ester copolymers,styrene/a-methyl styrene/acrylic acid copolymers, styrene/a-methylstyrene/acrylic acid/alkyl acrylate ester copolymers, styrene/maleicacid copolymers, vinyl naphthalene/maleic acid copolymers, vinylacetate/ethylene copolymers, vinyl acetate/fatty acid vinyl ethylenecopolymers, vinyl acetate/maleic acid ester copolymers, vinylacetate/crotonic acid copolymers, and vinyl acetate/acrylic acidcopolymers. Examples of the nonionic dispersants includepolyvinylpyrrolidone, polypropylene glycol, and vinylpyrrolidone/vinylacetate copolymers. Examples of the surfactant as the dispersant includeanionic surfactants such as sodium dodecylbenzenesulfonate, sodiumlaurate, and ammonium salts of polyoxyethylene alkyl ether sulfate; andnonionic surfactants such as polyoxyethylene alkyl ether,polyoxyethylene alkyl ester, polyoxyethylene sorbitan fatty acid ester,polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl amine, andpolyoxyethylene alkyl amide. In particular, from the viewpoint ofenhancing dispersion stability of the pigment, styrene/(meth)acrylicacid copolymers are preferred. The dispersant may be a water-insolublevinyl polymer that provides fixability and glossiness, such as onedisclosed in JP-A-2007-186641.

The ink composition of the invention preferably contains, as a wettingagent, one or more of polyols, sugars, and polyols having ethylene oxidechains. The addition of the wetting agent prevents drying of ink whenthe ink is applied to ink jet recording to suppress clogging in the headof an ink jet printer.

Examples of the wetting agent include polyols such as ethylene glycol,diethylene glycol, triethylene glycol, polyethylene glycol,polypropylene glycol, propylene glycol, butylene glycol,1,2,6-hexanetriol, thioglycol, hexylene glycol, glycerin,trimethylolethane, and trimethylolpropane; sugars such as sugaralcohols; and polyols having ethylene oxide chains such as ethyleneglycol monoethyl ether, ethylene glycol monobutyl ether, diethyleneglycol monomethyl ether, diethylene glycol monoethyl ether, diethyleneglycol monobutyl ether, triethylene glycol monomethyl ether, triethyleneglycol monoethyl ether, and triethylene glycol monobutyl ether. One ormore of them are used.

The ink composition of the invention preferably contains, as apenetrant, one or more of pyrrolidones, alkanediols, and glycol ethers.The addition of the penetrant can enhance wettability to a recordingmedium and enhance permeability of the ink. Examples of the penetrantinclude pyrrolidones such as 2-pyrrolidone and N-methyl-2-pyrrolidone;alkanediols such as 1,2-pentanediol and 1,2-hexanediol; and glycolethers such as ethylene glycol monomethyl ether, diethylene glycolmonoethyl ether, diethylene glycol monobutyl ether, triethylene glycolmonobutyl ether, propylene glycol monobutyl ether, and dipropyleneglycol monobutyl ether. One or more of them are preferably used.

In addition, each ink composition of the invention preferably contains,as a surfactant, at least one compound selected from the groupconsisting of acetylene glycols and polysiloxanes. The addition of thesurfactant can enhance wettability to a recording medium and enhancepermeability of the ink.

Furthermore, each ink composition of the invention may contain anorganic solvent having a low boiling point, from the viewpoint ofshortening the time for drying the ink. Examples of the low boilingpoint organic solvent include methanol, ethanol, n-propyl alcohol,iso-propyl alcohol, n-butanol, sec-butanol, tert-butanol, iso-butanol,and n-pentanol, and one or more of them are used. In particular,monovalent alcohol is preferred.

Each ink composition of the invention preferably contains componentssuch as the above-described pigment, dispersant, wetting agent, lowboiling point organic solvent, penetrant, and surfactant and containswater as the balance. The water is preferably pure water or ultrapurewater, such as ion-exchanged water, ultrafiltrated water, reverseosmosis water, or distilled water. In particular, sterilization of thewater by ultraviolet irradiation or hydrogen peroxide can preventincidence of molds or bacteria over a long period of time, and thereforesuch sterilized water is preferred.

Each ink composition of the invention may further contain additivesaccording to need, for example, a fixing agent such as water-solublerosins, a fungicide or antiseptic such as sodium benzoate, anantioxidant or ultraviolet absorber such as allophanates, a chelatingagent, an oxygen absorber, or a pH adjuster. One or more of them areused.

A preferred aspect of the magenta ink composition in the inventionprepared on the basis of above will be described below.

A diluted aqueous solution (10000 times or less) of the magenta inkcomposition in the invention preferably has an L* value of 60 or moreand a b* value of −17 or less when the a* value calculated from thevisible absorption spectrum is 80, according to the CIE standard.

In addition, a diluted aqueous solution (10000 times or less) of themagenta ink composition in the invention preferably has an a* value of11.5 or more and a b* value of -5.5 or less when the L* value calculatedfrom the visible absorption spectrum is 94, according to the CIEstandard.

The above-mentioned value ranges can be achieved by controlling thequinacridone solid solution pigment in the magenta ink composition so asto have specific components and blending ratios. In the above-mentionedvalue ranges, the magenta ink composition can have further excellentcolor reproduction in red and violet regions of high saturation and highbrightness, and can exhibit excellent color reproduction in a dark blueregion when it is used in an ink set as a combination with a cyan inkcomposition.

Furthermore, in the above, the L* value, the a* value, and the b* valueof the CIE standard calculated from a visible light absorption specimencan be obtained by measuring the transmittance with, for example, aU3300 Hitachi spectrometer under conditions of a scanning speed of 600nm/min, a measurement wavelength range of 380 to 800 nm, and a slitwidth of 2.0 nm and performing calculation in a D65 light source and aviewing angle of 2 degrees.

In addition, the magenta ink composition in the invention preferably hasan L* value of 96 or more and an a* value of 7.5 or more of the CIEstandard calculated from the visible absorption spectrum in an aqueoussolution of 2×10⁻³ g/L pigment. The above-mentioned value ranges can beachieved by controlling the quinacridone solid solution pigment in themagenta ink composition so as to have specific components and blendingratios. Since the quinacridone solid solution pigment has excellentchromogenicity, high color reproduction can be achieved in highsaturation and high brightness region even in a relatively low pigmentconcentration. Since excellent color reproduction can be achieved evenin a relatively low pigment concentration, an increase in viscosity dueto a high pigment concentration can be avoided. Therefore, even if thepigment concentration is relatively low, the magenta ink composition canexhibit excellent color reproduction in red and violet regions of highsaturation and high brightness.

In the case that the magenta ink composition of the invention contain aquinacridone solid solution pigment, the quinacridone solid solutionpigment preferably contains a pigment dispersion prepared by a processincluding a step of preparing a kneaded pigment by kneading thequinacridone solid solution pigment at a temperature higher than 120° C.

The magenta ink composition preferably contains a pigment dispersionprepared by a process including steps of preparing a kneaded pigment bykneading the quinacridone solid solution pigment at a temperature higherthan 120° C. and subjecting a composition containing the kneaded pigmentto dispersion treatment.

The process preferably further contains a step of ultrafiltrationclassification after the dispersion treatment.

A solid solution is very rapidly dispersed and is excellent inproductive efficiency. However, rapid dispersion causes clogging anduneven chromogenicity. Accordingly, the kneading treatment previous tothe microparticle dispersion is effective for preventing clogging.Furthermore, the ultrafiltration classification is effective forpreventing unevenness in color. The kneading treatment andultrafiltration classification can be carried out by the methodsdescribed in W02007/058245.

3. Ink Set

The ink set of the invention is preferably composed of at least fourcolors of a yellow ink composition, a magenta ink composition, a cyanink composition, and a black ink composition, from the point of enablingcolor reproduction in a broad range.

When the ink set of the invention includes a yellow ink composition anda black ink composition, the color materials are not particularlylimited, but examples of the color material contained in the yellow inkcomposition include C.I. pigment yellows 1, 2, 3, 12, 13, 14, 16, 17,73, 74, 75, 83, 93, 95, 97, 98, 109, 110, 114, 120, 128, 129, 138, 150,151, 154, 155, 180, 185, and 213. Examples of the color materialcontained in the black ink composition include carbon blacks (C.I.pigment black 7) such as furnace black, lampblack, acetylene black, andchannel black; metals such as copper oxides and iron oxides (C.I.pigment black 11); and organic pigments such as aniline black (C.I.pigment black 1), and carbon black has a relatively small specificgravity to hardly precipitate in water and therefore is preferred forink jet. These may be used alone or as a mixture. Specifically, carbonblack pigments are available, for example, from Mitsubishi ChemicalCorporation as No. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52,MA7, MA8, MA100, No. 2200B, or the like; from Columbia Chemicals Companyas Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven700, or the like; from Cabot Corporation as Regal 400R, Regal 330R,Regal 660R, Mogul L, Mogul 700, Monarch 800, Monarch 880, Monarch 900,Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, or the like; andfrom Degussa Company as Color Black FW1, Color Black FW2, Color BlackFW2V, Color Black FW18, Color Black FW200, Color Black 5150, Color Black5160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U,Special Black 6, Special Black 5, Special Black 4A, Special Black 4, orthe like. The components and their preparation of the yellow inkcomposition and the black ink composition can be carried out as in themagenta ink composition.

4. Recording Method and Recording Apparatus

The application of the ink set of the invention is not particularlylimited and can be applied to various types of ink jet recordingsystems. Examples of the ink jet recording systems include thermaljet-type ink jet, piezoelectric-type ink jet, sequential ink jet, rollerapplication, and spray application. In addition, the ink set of theinvention can be applied to, for example, recording apparatuses to whichthe recording systems mentioned above are applied.

In the invention, a recording medium to which droplets from the ink setof the invention adhere is preferably glossy paper for ink jetrecording. Here, the term “glossy paper” refers to plain paper having asurface provided with an ink-receiving layer excellent in surface glossby specific coating. In general, the glossy paper is cast-coated glossypaper having a surface provided with gloss by forming an ink-receivinglayer by casting or polymer-coated gloss paper having an ink jetrecording layer whose main component is a resin. In addition, as otherpolymer-coated gloss paper, a recording medium provided with an electrobeam curable resin can be used.

Examples

The invention will be described in detail below with reference toExamples, but is not limited thereto.

1. Preparation of Each Ink Composition (Cl, C2, C3, M1, M2, Yl, K1)

As shown in the following Table 1, cyan ink compositions (C1, C2, andC3), magenta ink compositions (M1 and M2), a yellow ink composition(Y1), and a black ink composition (K1) were prepared. In Table 1, thecontent of each component in the compositions is represented by mass %,the “dispersant” is a styrene/acrylic acid copolymer, and the“surfactant” is BYK-348 manufactured by BYK Chemie Japan K.K.

Furthermore, the quinacridone solid solution pigment contained in themagenta ink composition M2 was a solid solution formed of γ-type P.V.19and P.R.202 at a mass ratio of 70:30. The hue of the resulting solidsolution pigment showed a magenta color, but the X-ray diffractionpattern thereof was different from that of a mixture of γ-type P.V.19and P.R.202.

TABLE 1 C1 C2 C3 M1 M2 Y1 K1 Pigment P.B. 15:3 P.B. 60 P.B. 15:6 P.V. 19Solid solution P.Y. 74 Carbon 4.0% 4.0% 4.0% 5.0% (γ-type 3.5% blackP.V. 19/P.R. 202) 2.0% 5.0% Dispersant 2.4% 2.4% 2.4% 2.7% 2.7% 2.8%1.0% Glycerin 9.0% 9.0% 9.0% 9.7% 11.0%  14.0%  13.0%  1,2-hexanediol5.0% 5.0% 5.0% 2.5% 2.5% 5.0% 8.0% Triethanolamine 0.9% 0.9% 0.9% 0.9%0.9% 0.9% 0.9% Surfactant 0.5% 0.5% 0.5% 0.8% 0.8% 0.5% 0.3% Ultrapurewater balance balance balance balance balance balance balance Total100%  100%  100%  100%  100%  100%  100% 

2. Evaluation of Ink Set

Printing was carried out using an ink jet printer (“PX-5500”,manufactured by Seiko Epson Corporation). An exclusive ink cartridge forcyan (Model: ICC37, manufactured by Seiko Epson Corporation), anexclusive ink cartridge for magenta (Model: ICM37, manufactured by SeikoEpson Corporation), an exclusive ink cartridge for yellow (Model: ICY37,manufactured by Seiko Epson Corporation), and an exclusive ink cartridgefor black (Model: ICBK33, manufactured by Seiko Epson Corporation) ofthe printer were filled with the ink compositions in combinations shownin Table 2 to configure ink sets of Examples and Comparative Examples.

TABLE 2 Ink set Cyan Magenta Yellow Black Comparative C1 M1 Y1 K1Example 1 Example 1 C2 M1 Y1 K1 Example 2 C3 M1 Y1 K1 Comparative C1 M2Y1 K1 Example 2 Example 3 C2 M2 Y1 K1 Example 4 C3 M2 Y1 K1

The thus prepared ink cartridges were mounted on the printer, and aprinting test was carried out using photographic gloss paper (“photopaper (gloss)” manufactured by Seiko Epson Corporation) by printing acolored solid pattern at a duty of 85% or less.

Here, the yellow and black inks were used for finely adjusting thebrightness.

In the specification, the term “duty” refers to the value calculatedfrom the following equation:

Duty (%)=(actual number of printed dots)/[(verticalresolution)×(horizontal resolution)]×100

(wherein, the “actual number of printed dots” denotes the actual numberof printed dots per unit area, the “vertical resolution” and the“horizontal resolution” each denote resolution per unit area, and a dutyof 100% indicates the maximum ink mass of a monochromic color perpixel).

The CIE/L*a*b* values of the resulting printed matter were measuredusing a colorimeter (Spectrolino, manufactured by GretagMacbeth GmbH) incompliance with JIS Z8729. FIG. 1 shows the gamuts (color reproductionranges) at L*=20 in Examples 1 and 2 and Comparative Example 1, and FIG.2 shows the gamuts at L*=20 in Examples 3 and 4 and Comparative Example2. The “VM” in FIG. 2 corresponds to the above-described magenta ink M2.

As obvious from FIG. 1, the color reproduction range of the blue regionin a dark portion of an L* of 20 or less was significantly extended byusing a combination of a cyan ink composition containing P.B.15:6 orP.B.60 as the pigment and a magenta ink composition containing aquinacridone-based pigment, compared to the range in the case of using acyan ink composition containing P.B.15:3, which has been widely used. Inaddition, as shown in FIG. 2, a color having an a* value of 30 or moreand a b* value of -75 or less at an L* value of 20 or less wasreproduced by especially using a combination of a cyan ink compositioncontaining P.B.15:6 as the pigment and a magenta ink compositioncontaining a quinacridone solid solution pigment (VM) as the pigment.Such a color could not been reproduced by known methods.

1. An ink set comprising: a cyan ink composition containing C.I. pigmentblue 15:6 as a pigment; and a magenta ink composition containing atleast one quinacridone pigment selected from the group consisting ofC.I. pigment violet 19, C.I. pigment red 122, C.I. pigment red 202, andC.I. pigment red 209, or a quinacridone solid solution pigment formed ofat least two selected from the above group, as a pigment.
 2. The ink setaccording to claim 1, wherein the pigment contained in the magenta inkcomposition is a quinacridone solid solution pigment formed of at leasttwo selected from the group consisting of C.I. pigment violet 19, C.I.pigment red 122, C.I. pigment red 202, and C.I. pigment red
 209. 3. Theink set according to claim 2, wherein the pigment contained in themagenta ink composition is a quinacridone solid solution pigment formedof C.I. pigment violet 19 and C.I. pigment red
 202. 4. The ink setaccording to claim 3, wherein the quinacridone solid solution pigment isformed such that the weight of the C.I. pigment violet 19 is larger thanthat of the C.I. pigment red
 202. 5. The ink set according to claim 3,wherein the quinacridone solid solution pigment is formed such that theweight ratio of the C.I. pigment violet 19 to the C.I. pigment red 202is from 70/30 to 50/50.
 6. The ink set according to claim 1, wherein theC.I. pigment violet 19 contained in the quinacridone solid solutionpigment is a γ-type.
 7. A recording apparatus comprising the ink setaccording to claim 1.